It depends on how you define energy. A number of theorists, Hawking among them, have suggested the 'zero energy' concept. It is attractive because it avoids the problem of a universe that sprang from nothing to something. The universe consists of positive energy (matter) and negative energy (gravity) whose total is exactly zero! This is a valid mathematical solution for the Hamiltonian density of the universe in GR. The issue is, however, complex and different answers are possible depending on the geometry of space time.

It is, however, easier to forget about positive and negative energy and fall back on thermodynamics saying, as Nenad did, that the total energy of the universe is constant and unchanging [although it could still be zero].

A zero point energy is exactly at a center point between two extremities of the infinity i.e. -∞ to +∞ and both these extremeties of the universe are always present.
Breaking the zero equally or symmetrically on to both sides, consumes energy that you may call energy taken by the system, where as collapsing these both symmetrical sides back to zero will return the energy back. Now in one case it is positive energy while in another case it will be negative. Think yourself as to which will be positive and which one negatuve ??

Chronos this is a very good link. If you did not put it on the A&C Sticky thread (for handy references) already then I will

I have heard Alex Filippenko lecture---he is outstanding, with good slides clear explanations humor and verve----the co-author Jay Pasachoff is
a very successful textbook writer in general astro, with many books.

I was worried that we didnt seem to come to grips with this zero energy puzzle in Curious other thread (Closed Flat or Open?) where Curious asked it as a follow up question.

but now the question has been addressed.

BTW it is still not completely clear to me how the U does this. but it is gradually getting more clear

I'm not a scientist - but this subject interests me. It seems to me that if the universe is infinite, then the total energy must be zero as

e=mc2

thererfore to work out the energy we can say

mc2
____________ = 0
infinity

As anything over infinity tends to 0 - whats my flaw here?

This only gives you the average distribution of the energy over the volume of the Universe, but not the total energy in the Universe, as mc[SUP2[/SUP] is equal to e, so therefore you have calculated the total energy divided by the "infinite" volume of the Universe, not the total energy itself

Chronos this is a very good link. If you did not put it on the A&C Sticky thread (for handy references) already then I will

I have heard Alex Filippenko lecture---he is outstanding, with good slides clear explanations humor and verve----the co-author Jay Pasachoff is
a very successful textbook writer in general astro, with many books.

I was worried that we didnt seem to come to grips with this zero energy puzzle in Curious other thread (Closed Flat or Open?) where Curious asked it as a follow up question.

but now the question has been addressed.

BTW it is still not completely clear to me how the U does this. but it is gradually getting more clear

Perhaps many quantum fluctuations occurred before the birth of our universe. Most of them quickly disappeared. But one lived sufficiently long and had the right conditions for inflation to have been initiated. Thereafter, the original tiny volume inflated by an enormous factor, and our macroscopic universe was born. The original particle-antiparticle pair (or pairs) may have subsequently annihilated each other – but even if they didn’t, the violation of energy conservation would be minuscule, not large enough to be measurable.

I think there is a problem with this idea. If there were quantum fluctuations before the birth of our universe then in what spacetime did they occur? In order for one or many quantum fluctuations as the article suggests, to occur, doesn't there have to be a pre-existing spacetime volume in which it occurs? This seems to imply that a single qf in a preexisting spacetime was a center point from which our universe expanded but I think we all agree that our universe doesn't have a center. This is confusing. It seems to be some kind of circular argument, like which came first the chicken or the egg.

I can't believe you guys are seriously arguing about this stuff. The very definition of "energy" voids the possibility of "zero energy" (Hawkings is a media clown). In fact, you can't even have negative energy. What would negative energy be? - "The ability to undo work?" Which would BE work, of course.

How God Creates - don't worry about the use of the word "God". It gets explained in the post.

He is talking about the reduction of energy after coming closer to the planet from outer space. The available energy within a system can be reduced. That yields equations with negative signs because they represent a reduction from a prior state of the system. It doesn't mean the existence of negative energy.

The concept of negative energy is like the concept of a negative circle or negative light. You can have negative directions and sizes, but not negative existences.

I can't believe you guys are seriously arguing about this stuff. The very definition of "energy" voids the possibility of "zero energy" (Hawkings is a media clown). In fact, you can't even have negative energy. What would negative energy be? - "The ability to undo work?" Which would BE work, of course.

Credibility is subjective to you. Logic is the issue. Negative energy, required to obtain a "zero energy", is the same concept as "negative existence". Something either exists or it doesn't. There is no "negative" to existence other than an existence having reverse properties nominally declared "negative". But the reverse properties of energy, the ability to do work or make change, would not be merely the inability to do work or make change, but the ability to un-work and un-change. But un-working is working and un-changing is change, merely in a different direction at best and thus it is the same abstract concept. There is no "un-working" concept. You either cause change or you do not. There is no negative concept to change.

Negative energy particles are falling into black holes by the trillions that's the only way to pull mass out of them. And yes it uncauses the original matter to unexist an undo itself. Even a "clown" who hold's Newton's chair knows that.